Physical meaning of kinetics parameter “lifetime” used in the new multi-point reactor kinetics equations derived using Greenʹs function

The reactor kinetics parameter I which is used in the new multi-point reactor kinetics equations derived using Greenʹs function is shown to have a physical meaning of neutron production time which can be calculated by the Monte Carlo method, although the corresponding reactor kinetics parameter used in the conventional one-point reactor kinetics equations derived using an adjoint function as a weighting function has, in general, no clear physical meaning.